Known as an example of conventional image acquisition devices is a device described in Patent Literature 1. This device splits light from a subject with a half prism and receives the light with a photoelectric transducer constituted by a two-dimensional image pickup element such as a CCD area image sensor. A control circuit for the photoelectric transducer has a scan area setting unit which can arbitrarily set two scan areas for two-dimensionally scanning the light-receiving surface. Focusing control is executed according to a focus deviation signal of the light received by the two scan areas set by the scan area setting unit.